Some microphones are of a stick type and include replaceable microphone units. A typical microphone including a replaceable microphone unit has an element part and a power module part, for example. The element part includes the microphone unit. The power module part includes a circuit board for processing electrical signals from the microphone unit.
Some microphones have been proposed each including a movable joint coupled between the element part and the power module part to make the sound collecting axis of the microphone unit adjustable (for example, the “Capsule Swivel GVC” available from Schoeps GmbH, Karlsruhe, Germany).
The joint used in the Capsule Swivel GVC is a so-called swivel joint including a first unit to be coupled to the element part and a second unit to be coupled to the power module part. The first unit includes a hemispherical first movable member. The second unit includes a hemispherical second movable member. The first movable member and the second movable member are composed of metal having the same shape.
The first movable member is attached to the second movable member. The open end of the first movable member abuts on the open end of the second movable member. The first movable member is rotatable relative to the second movable member along the circumferential direction of the second movable member within a predetermined range of angle. The second movable member is rotatable relative to the first movable member along the circumferential direction of the first movable member within a predetermined range of angle.
Thus, the first unit and the second unit are rotatable relative to each other, having the first movable member and the second movable member function as movable parts. When the movable parts rotate relative to each other, the open end of the first movable member and the open end of the second movable member slide on each other.
As described above, the first movable member and the second movable member are composed of metal. Thus, the open end of the first movable member abuts on the open end of the second movable member at a limited number of points. As the number of points of contact increases, the electrical connection between the first movable member and the second movable member becomes more certain, whereas the frictional force between the first movable member and the second movable member increases. As this frictional force increases, the movability of the first movable member decreases, whereas the force (hereinafter referred to as “fixing force”) of fixing the rotational position (the angle of the first movable member from the second movable member) of the first movable member relative to the second movable member increases. In other words, the frictional force between the first movable member and the second movable member affects the electrical connection, movability, and fixing force in the movable parts (between the two units).